Clarification on Allocation Method Override in Product System Calculations

Question

Hello everyone,

I have a question regarding allocation methods in openLCA:

If I set the allocation method for individual processes (e.g., economic allocation), but then, when calculating the impacts for a product system, I choose a different allocation method (e.g., physical allocation) in the calculation setup, which allocation method will openLCA use for the calculation?

Does the method selected at the product system level override the allocation methods defined in the individual processes, or does it only apply if the process does not have an allocation method assigned?

Additionally, what happens if some processes cannot be allocated by the method chosen at the product system level (e.g., physical allocation is not possible due to incompatible units)?

Thank you in advance for your help and clarification!

Answer 1

Hi qtu,

thanks for reaching out. Yes, the allocation method will overwrite what was stated in the individual processes. To make it clearer, openLCA always refers to the allocation factors from the respective "allocation" tab on the process level. Everything you see there will be used as it is in the product system. Moreover, make sure you calculate the allocation factors or update them. However, if you have incompatible units, openLCA does not perform allocation and there might be no allocation performed on process level. Hence, there is also no allocation happening for this process during the result calculation of the product system.

Hope this helps

p.s. the openLCA manual helps you on this topic, but also a short test in the software tells you the answer quite quickly